Engine - Timing Gear Noise (Knock)
Number 86-6(Gasoline)-64 Date 10/86Subject: ENGINE TIMING GEAR NOISE (KNOCK)
1985-86 6000, FIREBIRD, GRAND AM, AND FIERO MODELS WITH 2.5L L4 ENGINES
IF AN ENGINE HAS A KNOCK AND THE PRELIMINARY DIAGNOSIS IS A "CAM GEAR KNOCK", USE THE NORMAL PROCEDURE DESCRIBED IN BULLETIN 85-6(Gasoline)-39 TO CHECK CAM SHAFT END CLEARANCE AND GEAR BACKLASH.
MEASURE THE BACKLASH AT POSITIONS OUTSIDE THE TWO RETAINER PLATE ACCESS HOLES AND AT TWO OTHER AREAS 90 DEGREES FROM THESE HOLES.
NOTE: CRANK PULLEY MUST BE INSTALLED AND TORQUED BEFORE MAKING BACK LASH MEASUREMENTS.
IF END CLEARANCE IS NOT BEYOND .0015" (.0038 CM) TO .0050" (.0127 CM) AND BACKLASH IS NOT BEYOND .0005" (.0013 CM) TO .0095" (.0241 CM) AND THE CAM AND CRANK GEARS ARE NOT DAMAGED, THE GEARS ARE NOT CAUSING THE KNOCK. EXAMINE THE ENGINE FOR OTHER SOURCES OF KNOCK.
IF END CLEARANCE IS LESS THAN .0015", REPLACE THE SPACER RING; IF IT EXCEEDS .0050", MAKE CERTAIN THE GEAR IS SEATED PROPERLY AGAINST THE SPACER AND IF IT STILL EXCEEDS .0050", REPLACE THE THRUST PLATE.
IF BACKLASH IS LESS THAN .0005", OR GREATER THAN .0095", REPLACE THE CAM AND CRANK GEARS.
RECORD THE END CLEARANCE AND BACKLASH READINGS ON A TAG AND ATTACH IT TO THE REPLACED PARTS.
REVISED TIME ALLOWANCES FOR DIAGNOSIS, R AND R AND/OR REPLACEMENT OF CAMSHAFT TIMING GEAR OR CAMSHAFT ARE AS FOLLOWS:
OPERATION VEHICLE SERIES
NUMBER A F N P
GEAR, CAMSHAFT - REPLACE J0840
7.3 6.2 9.3 9.1
CAMSHAFT - REPLACE J0850
ADD:
WITH A/C .3 .4 .6 .9
WITH CRUISE CONTROL .2 .2 .1
REPLACE CRANK GEAR .2 .2 .2 .2